The sprawling Ogallala Aquifer in the Great Plains provides freshwater for roughly one-fifth of the wheat, corn, cattle and cotton in the United States. But key parts of the underwater aquifer are being depleted faster than they can be recharged by rain (see map).

Regions where the water level has declined in the period 1980-1995 are shown in yellow and red; regions where it has increased are shown in shades of blue. Data from the USGS (Wikipedia)

That raises a question: How long before those areas in decline run out of groundwater for farming?

A recent study in the Proceedings of the National Academy of Sciences tried to come up with an answer for the crucial Kansas section of the aquifer. At current rates of use, farming in that area is likely to peak by 2040 or so due to water depletion.

With better conservation techniques, western Kansas could probably stretch things out so that farm production doesn't peak until the 2070s. But avoiding any sort of peak altogether would require drastic measures — beyond anything contemplated today.

The depletion problem

Aquifers have taken on increasing importance in the last few years as U.S. food production has expanded and drought has become a nagging issue. In regions like western Kansas, where farmers haven't been getting enough rain for their crops, they've depended on irrigation, pulling up water from the Ogallala.

As a result, the aquifer is slowly getting depleted, with the water table dropping by as much as two feet per year in some counties. And once they drain, it could take hundreds or thousands of years for those ancient aquifers, which were first formed millions of years ago, to fully recharge with rainfall.

This isn't news to anyone in the region. As Brett Walton reports in great detail here, Kansas has been talking about how to save water for years. Farmers in the northwest part of the state, for instance, have recently agreed to reduce the amount of water they pump from the Ogallala by 20 percent over the next five years. Last year, the state legislature enacted a new system of water rights to provide incentives to conserve.

Cows take advantage of irrigation sprinklers in their field near Marcola, Ore. Wednesday July 29, 2009. (AP Photo/The Register-Guard, Kevin Clark)

That brings us to the latest PNAS study, led by David Steward of Kansas State University. Researchers found that 30 percent of the Kansas portion of the Ogallala Aquifer has already been pumped out, and another 39 percent will get used up in the next half-century at existing rates. Kansas, clearly, is on the fast track to depletion. As a result, agriculture production is likely to peak around 2040 and decline after that.

There's a way to alter that course, however. The study found that if farmers and other users could cut the amount of groundwater pumping by 20 percent immediately — that is, the cuts that farmers in the northwest have proposed — that could extend the life of the aquifer significantly. Farming wouldn't have to peak until the 2070s, and it would fall more gently thereafter.

That looks doable. Water use efficiency is already increasing by 2 percent per year, the study found, thanks to better crop genetics and irrigation techniques. And a separate paper this year from Kansas State University found that immediately cutting groundwater use in the region by 30 percent would be possible with existing technologies. The economic hit would be modest: In many cases, the gains from extending the life of the farmland would outweigh the upfront costs.

But now what if Kansas wanted to farm sustainably and keep its aquifer around forever? That's more daunting. As Steward and his colleagues found, farmers would have to cut their groundwater pumping by 80 percent today — to bring depletions in line with rainwater recharge. This would require a drastic reduction of corn and cattle production.

"That ain’t gonna happen," notes John Fleck, a journalist who has been tracking water issues out West for many years. (And credit to Fleck for calling our attention to the study in the first place.)

The authors of the PNAS study seem to agree that it's unlikely that farmers in the Plains would realistically cut water usage enough to make the aquifer last for all time. "Eventually," they conclude, "the southwest and northwest districts in Kansas will realize the fate emerging in the west central district, where shallower groundwater stores have resulted in decreased well yields, well abandonment, and conversion back to dryland." The key question is how long that day of reckoning can be put off.

Related:

-- Brett Walton's coverage of Ogallala water issues for Circle of Blue has been excellent. See here for his story on Kansas depletions.

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